The present invention relates to a guide vane for a turbo machine, such as an aircraft turbojet engine, in which the internal structure of the vane defines cooling air circuits.
Guide vanes for turbo machines, such as turbojet engines, are well known the art. A typical example is shown in U.S. Pat. No. 3,574,481 in which the interior of the vane accommodates a cooling air supply duct, which is formed separately from the vane. The interior walls of the vane form partitions which define cooling passages along the internal sides of the convex and concave sidewalls. The cooling air passes through the cooling air supply duct and into a turbulence chamber to cool the leading edge of the vane. Thereafter, the cooling air circulates through the circulation passages on both sides of the separate cooling air supply duct and is exhausted through openings formed in the trailing edge of the vane.
French Patent 2,290,569 also describes a guide vane having internal cooling means wherein a separate internal part defines cooling passageways and wherein an additional partition cuts the passageway between the swirl chamber and the circulation passageways on the convex side of the vane. The cooling air enters the turbulence chamber and is evacuated toward the trailing edge of the vane adjacent to the interior of the convex sidewall. A portion of the cooling air passing along the convex sidewall is evacuated through evacuation orifices located at the end of the air circulation passages through the convex sidewall near the leading edge.
These known vanes have cooling means which allow the cooling of the leading edge of the vane by forcing the cooling air against the internal portion of the leading edge. This causes the cooling air to be significantly heated which, in turn, causes the cooling air to poorly cool the sidewalls of the vane. In the aforementioned French patent, the air exiting through the evacuation orifices located at the end of the air circulation passages is also comparatively warm, so that it cannot thermally protect the outside surface of the convex sidewall. In addition, even through the internal structures of the known vanes include heat radiating surfaces which are swept by the cooling air, the heat exchange through such heat radiating surfaces is slight due to the small spacing between the separate cooling air ducts and the vane sidewalls.
Due to these limitations in the cooling of the vanes, the temperature of the gases exiting from the turbojet engine combustion chamber must be limited so as to not structurally weaken the vanes. Generally, the vanes immediately downstream of the turbojet engine combustion chamber are subjected to the highest thermal stresses. Since the turbojet engine performance increases as the exhaust gas temperature increases, the limitations of the exhaust temperature due to the inefficient cooling of the guide vanes imposes a severe limitation on the engine performance. Quite obviously, it would be beneficial to cool the guide vanes as much as possible so that they may withstand a higher exhaust temperature which results in increased performance of the turbojet engine.